French tax authorities are demanding hundreds of thousands of euros from the co-creator of Asterix, ruling that Albert Uderzo is a "simple illustrator" undeserving of the tax breaks authors enjoy.

To Asterix fans, he is half of the inspiration behind the plucky Gaul and his corpulent sidekick, Obelix, whose only fear is of the sky falling on their heads.

Mr Uderzo has been ordered to pay €203,000 euros (£171,000) in unpaid tax on the 24 Asterix comic books he and the late René Goscinny produced between 1959 and 1979.

France's tax office has ruled that Mr Uderzo, 84, cannot benefit from the country's authorial rights tax regime, which comes with an extra tax exemption, because it only applies to "people who have participated in writing the texts of the comic strip".

They consider he was responsible only for the drawings of the mustachioed heroes who valiantly resist their Roman invaders.

Mr Uderzo pledged to take on the might of the French taxman in the spirit of the comic book Gaul he brought to life.

"This is an injustice and a scandal," he said.

"The brutality and lack of respect with which, 51 years after creating Asterix, the tax authorities have 'woken up' to deny me the right to be co-author of my dear little Gaul – at my age I will not accept to be stripped of this title," he said.

Mr Uderzo said the taxman need only look at the original contract signed with the Darguad publishers. "It was stipulated that I signed off the drawings and René Goscinny the texts, but that we formed one single author," he said.

"Moreover, for each album, we met before getting stuck into the scenario to dream up a story. Goscinny worked according to my requirements and I to his," he said.

It was in this way that Mr Uderzo said he came up with the idea of Obélix's faithful dog, Dogmatix in the 10th album, Asterix and the Banquet.

Mr Uderzo has had to fight a series of battles in recent years. He has faced frequent criticism that the ten albums he illustrated and wrote after Goscinny's death in 1979 lack the wit and brio of the original series.

Then in 2009, his daughter, Sylvie, publicly accused him of selling Asterix's soul to big business, namely a giant publisher. Her father, she said, risked handing "this first victorious act of the invader against the indomitable Gauls" because of his "repudiation of all the values" Asterix stands for. The sale nevertheless went ahead.

Asterix comics sell roughly three million copies annually, with more than 325 million albums sold since the 1961 pilot.